INVESTIGATION ON DEFORMATION AND STABILITY OF CUT SLOPES USING LIQUID EQUILIBRIUM (LE) METHODS AND FINITE ELEMENT (FE) METHODS. (CASE STUDY ON THE MORKA GIRCHA CHENCHA ROAD PROJECT)

Abstract

Rapid urban development often requires cutting natural slopes, which can cause deformation and reduce slope stability. The main part of this study focuses on the the deformation and stability of cut slopes using Liquid Equilibrium Methods and Finite Element Methods which is achieved by conducting different types of field and laboratory tests. The objectives of this research were conceived to study in detail the cut-slopes stability condition of Morka Gircha Chencha road project. It was realized that detailed slope stability studies along this road section are very necessary to identify critical slope geometry and to provide the best preventive measures to minimize the slope instability problems. For the present study, a total of 48 analyses were carried out for six cut slopes with four slope angles; i.e. (1H: 1V), (1.5H: 1V), (2H: 1V), and (2.5H: 1V) before and after water saturation for each cut slope. The factor of safeties and slope deformation for the selected slope sections was determined for the different slope geometries and in the presence of water (saturated condition) using SLOPE/W, and PLAXIS-2D software. The comparison of the Liquid Equilibrium Methods shows that the Spencer, Bishop, and Morgenstern-Price Methods yield in most cases identical Factor of Safety (FOS). for circular slip surfaces. However, the Ordinary and Janbu methods underestimate the Factor of Safety (FOS). All Liquid Equilibrium Methods, except the Ordinary and Janbu Methods, estimate higher Factor of Safety than Finite Element analysis in PLAXIS-2D. Generally, it was observed from both PLAXIS-2D and SLOPE/W models that the provision of steep cut slope angles, the presence of a high proportion of fine soils, and migration of moisture from prolonged rainfall duration were the main reasons for the instability of the cut slopes under this study. Based on the results obtained from both PLAXIS-2D and SLOPE/W models, it can be concluded that flattening the slope angle from (1H: 1V) to 2.5H: 1V and above with lowering of the water table would be one of the techniques to stabilize the slope.